ABB ArcLimiter User guide

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TECHNICAL AND APPLICATION GUIDE
ArcLimiterTM
Arc flash mitigation solution for low
voltage equipment using UFES (ultra-
fast earthing switch)

2ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
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Many industries are facing internal
or external deadlines to implement
arc flash (AF) mitigation solutions
within their facilities. ABB now
offers ArcLimiterTM, an arc flash
mitigation solution that is unique
in the industry. It solves the LV arc
flash problem at the MV or LV
system level.

TECHNICAL AND APPLICATION GUIDE 3
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Table of contents
004 – 005 Introduction
006 Solidly grounded MV systems
007 – 008 Low resistance/grounded MV
systems
009 – 010 High resistance/grounded MV
systems
011 – 012 Ungrounded Delta MV systems
013 Summary of ArcLimiterTM solution
application scenarios
014 MV-LV transformers fed by MV
breaker
015 ArcLimiterTM solution application
at LV system level
016 Available UFES ratings

4ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Abbreviations used in this document
AF: arc flash
AWG: American Wire Gage
CLF: current limiting fuse
FLA: full load amperes
LV: low voltage
MV: medium voltage
PSE: primary switching element
QRU: quick release unit (of the UFES)
REA: ABB’s dedicated arc flash detection relay
SCC: short circuit capacity
SUS: secondary unit sub, MV-LV
51G: AC inverse time earth overcurrent relay
(residual method)
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This solution is appropriate for:
- Light and heavy industrial
- Commercial facilities
- Educational campuses
- Any facility applying primary
loop fed transformers with
fused MV switches (36 kV
limit), new or existing applica-
tions
- Facilities having MV to LV
transformers in the range of
750 KVA – 5000 KVA
To prove this solution concept, tests were per-
formed at a third-party test laboratory. During an
actual LV arc flash event (performed per IEEE
C37.20.7), the REA detected and responded to the
AF event, sending a closing signal to the UFES.
The REA is advertised to detect and close its out-
put trip contact within 2.5 milliseconds (ms). With
the current setting at 1.5x the CT primary rating
and the light detection adjustment at mid-range,
this third-party test proved the REA responded
within 1 ms.
This response placed negligible voltage on the
transformer primary, extinguishing the LV arc
flash quickly (approximately 4 ms). Test results in-
dicate the incident energy level peak was 0.5 cal/
cm2, which is well below the AF threshold of 1.2
cal/cm2, where PPE is required.
A note on the CLF application is in order. A fuse
will become current limiting when the magnitude
of amperes through it is large enough to fully in-
terrupt in ¼ cycle or less, i.e., the fault waveform’s
peak is never reached. In general, for each appli-
cation with an applied UFES and MV E rated fuse,
the applying engineer needs to obtain the SCC (in
amperes) available at the upstream MV BUS. The
MV E rated fuse will reach its current limiting
threshold (¼ cycle interruption) when the ratio of
SCC to fuse full load ampere rating is 25 times at
a minimum. If the ratio is less than 25, the fuse
will take many cycles to fully interrupt. With the
UFES closed, the MV BUS is now at zero volts,
negatively impacting plant operations.
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ArcLimiterTM
Introduction
Many industries are facing internal or external deadlines to implement
arc flash (AF) mitigation solutions within their facilities. ABB now
offers ArcLimiterTM, an arc flash mitigation solution that is unique in
the industry. It solves the LV AF problem at the MV or LV system level.
Many industries have internal distribution system configurations as
shown in Figure 1. The REA and UFES are ABB product additions to
this typical configuration that comprise the ArcLimiter AF mitigation
solution.

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
BONDING JUMPER
TECHNICAL AND APPLICATION GUIDE 5
LV starters can drop out while we are waiting for full
fuse interruption. The CLF interruption time deter-
mines when the MV BUS returns to nominal operat-
ing voltage.
Consider the following two examples for illustration
(in either case, the LV AF problem is solved equally
well):
• System SCC= 10,000A; CLF is a 150E; ratio of the
SCC to the fuse FLA rating is 67. Fuse will inter-
rupt in ¼ cycle. Operations should not be im-
pacted.
• System SCC= 4,600A; CLF is a 200E; ratio is 23.
Fuse will interrupt in cycles. Operations could be
impacted and the plant needs to be informed up-
front.
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01 Internal distribution
system configuration
Post testing analysis revealed that MV system
grounding has an impact on overall system behavior
in case of an AF and applying a UFES. This applica-
tion note addresses system grounding configura-
tions and how to technically apply the UFES, mini-
mizing any reliability issues for customers’ plants.
Each MV grounding method is addressed.

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
BONDING JUMPER
6ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
On a solidly grounded MV system, shown in Figure
2, the ArcLimiter application for LV AF mitigation is
proven very effective by test. The UFES closes all
three phases to ground simultaneously with some
minor contact bounce. At this point, the LV AF is
over.
Depending upon UFES closing time and phase se-
quence, phases A and B fuses melt in 1 ms (MV sys-
tem voltage recovery starts) with full CLF interrup-
tion by 1.5-2 ms. The actual CLF interrupting time is
dependent upon the MV system fault availability
(many times referred to as SCC). The higher the
SCC, the faster the CLF interruption, the shorter du-
ration of the fault induced voltage dip, the less im-
pact on other on-going operations.
When phases A and B CLF fully interrupt, the entire
phase C current briefly appears as a zero sequence
current on the traces. The only path for fault current
is through the phase C fuse, to UFES phase C PSE,
to transformer grounded neutral. Since there is no
impedance in that path, the fault current flow is
high, only limited by the transformer’s short circuit
impedance.
Since phase C is delayed by 120 degrees, about 5
ms (assuming a 60 Hz system), in order for the
phase C fuse to melt, those amps will not flow via
phases A and B fuses, which are already open, but
back to the source neutral. The UFES to ground
bonding jumper can be small thermally, approxi-
mately #2 AWG, since it only has to carry current for
5 ms.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with all three
PSEs.
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Solidly grounded MV systems
On a solidly grounded MV system, the ArcLimiter application for LV arc
flash mitigation is proven very effective by test.
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02 solidly grounded
MV system
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01

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
51G
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
(normally closed)
REA
BONDING
JUMPER
AC
B
51G-2
51G-1
GROUND
FAULT
PATH
TECHNICAL AND APPLICATION GUIDE 7
If the MV system is not solidly grounded, but low
resistance neutral grounded (Figure 3) the applica-
tion of the ArcLimiter solution needs to change.
The UFES closes all three phases to ground, simul-
taneously, when triggered. At this point, the LV AF
is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B fuses melt in 1 ms (MV sys-
tem voltage recovery starts) with full CLF interrup-
tion by 1.5-2 ms (SCC dependent). When phase A
and B CLF clear, the entire phase C current appears
as a zero sequence current on the test traces. There
is a large reduction in phase C fault current once
phases A and B CLF open.
The only path for fault current is through the phase
C fuse, to UFES phase C PSE, to the transformer’s
neutral, but is now limited by the source neutral re-
turn path’s resistance (Figure 4).
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Low resistance/grounded MV
systems
If the MV system is not solidly grounded, but low resistance neutral
grounded, the application of the ArcLimiter solution needs to change.
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03 MV system is not
solidly grounded,
but low resistance
neutral grounded
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04 Path for fault current
is through the phase C
fuse, to UFES phase C
PSE, to the transformer’s
neutral, but is now lim-
ited by the source neutral
return path’s resistance
—
03
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04

8ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Typically, in industrial plants, that ground fault
value can be limited to 200-600 A and in power
plants up to 1200 A. Phase C could remain energized
to the transformer primary for an extended time
and since most of the plant’s SUS are delta-wye, all
three transformer phases have the same evenly ap-
plied potential. Since there is no potential differ-
ence between the delta windings, there is no cur-
rent flow, therefore, there is no induction to
generate secondary potential. With no supporting
secondary potential, the LV AF collapses in micro-
seconds.
However, a sustained bolted line-to-ground phase C
fault on a low resistance grounded system will be
detected and tripped by the upstream 51G-1 or
51G-2 protection relay “x” seconds later. Review the
ground return path in Figure 4. This action shuts
down the entire MV BUS resulting in poor reliability
for customers’ plants. The 51G-1 or 51G-2 will be
faster than a sustained high ground fault value (say
1200 A) through the CLF.
To prevent this reliability issue, the MV SWITCH
should be installed (or retrofitted) with a shunt trip
activated by one of the QRU1’s trip out contacts
Phase A and B CLF will still interrupt in about the
same timeframe, about 1-2 ms, since they are in se-
ries through the closed PSEs. Phase C may not in-
terrupt. The upstream 51G-1 or 51G-2 will not see
ground current within its pick up range.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with the three
PSEs. The UFES to ground bonding jumper can be
small thermally, approximately #2 AWG, since it only
has to carry current for 5 ms.
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Low resistance/grounded MV
systems

UFES
MV “E” RATED FUSE
MV BUS
OIL or DT
XFMR
LV EQUIPMENT
MV SWITCH
(normally closed)
REA
10A
BONDING JUMPER
UFES: 3 PSEs
(CLOSED)
MV “E” RATED FUSES
MV BUS (3 PHASE)
OIL or DT
XFMR
LV EQUIPMENT
(3 PHASE)
MV SWITCH
(normally closed)
REA
BONDING
JUMPER
AC
B
GROUND
FAULT
PATH
HIGH RESISTANCE
TECHNICAL AND APPLICATION GUIDE 9
If the MV system is high resistance neutral
grounded (Figure 5) the application of the Ar-
cLimiter solution needs to change. These types of
systems are typically applied in older industrial
plants, feeding a process. A single line to ground
fault does not cause major damage and the MV
switchgear breakers usually do not have ground
fault protection. Indications of a ground fault are
usually detected via installed voltmeters. The oper-
ating process continues as a plant benefit.
The UFES closes all three phases to ground simulta-
neously. At this point, the LV AF is essentially over.
Depending upon UFES closing time and phase se-
quence, phase A and B CLF melt in 1 ms (MV voltage
system recovery starts) with full CLF interruption
by 1.5-2 ms (SCC dependent). When phases A and B
CLF clear, the entire phase C current (now very lim-
ited) appears as a zero sequence current.
The only path for fault current is through the phase
C CLF to UFES phase C PSE to transformer’s neu-
tral, but is now very limited by the source neutral
return path’s resistance (Figure 6).
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High resistance/grounded MV
systems
If the MV system is high resistance neutral grounded, the application of
the ArcLimiter solution needs to change.
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05 MV system is
high resistance
neutral grounded
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06 Path for fault current
is through the phase C
CLF to UFES phase C PSE
to transformer’s neutral,
but is now very limited
by the source neutral
return path’s resistance
—
05
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06

10 ARCLIMITERTM ARC FLASH MITIGATION SOLUTION FOR LV USING UFES
Typically, in industrial plants, the maximum high im-
pedence ground fault current flow value is limited
to 10 A. Phase C could remain energized to the
transformer primary for an extended time and,
since most of the plant’s SUS are delta-wye, all
three transformer phases have the same equally ap-
plied potential. Since there is no potential differ-
ence between the delta windings, there is no cur-
rent flow, therefore, there is no induction to
generate secondary potential. With no supporting
secondary potential, the LV AF collapses in micro-
seconds.
However, having a sustained bolted line-to-ground
phase C 10 A fault will activate the plant’s ground
fault alarm system. Maintenance would be chasing
the wrong problem. To prevent this nuisance alarm,
the MV SWITCH should be installed (or retrofitted)
with a shunt trip activated by one of the QRU1’s trip
out contacts.
Two of the CLFs will still interrupt in about the same
timeframe, about 1-2 ms, Phase C CLF may not in-
terrupt. This prevents the false ground fault alarms.
Upon UFES operation, all three fuses should be re-
placed, since the phase C fuse may be damaged by
microsecond internal arcing, along with the three
PSEs. The UFES to ground bonding jumper can be
small, approximately #2 AWG, thermally, since it
only has to carry current for 5 ms.
—
High resistance/grounded MV
systems